1. Field of the Invention
The present invention generally relates to stage apparatuses. More particularly, the present invention relates to a stage apparatus whereby micro moving control is stably implemented at the time when a holding member configured to hold a subject goes up and down in a Z axial direction.
2. Description of the Related Art
In a stage apparatus, a subject wafer is positioned with high precision in response to carrying the wafer and holding the wafer by a wafer holding member having a vacuum chuck or an ESC (Electrostatic Chuck). Therefore, the wafer holding member is operated in a Z axial direction and a θ z direction around the Z axial direction so that positioning control for adjusting position of the wafer is implemented.
In the stage apparatus, a pair of Z axis actuators is arranged with 180 degree gaps therebetween in the circumferential direction. The pair of Z axis actuators implements fine adjustment of a height position of the wafer to correspond to focal length (focal depth) of a CCD (Charge Coupled Device) camera for imaging the wafer. In addition, the wafer holding member is supported by a rotation supporting member mounted on a XY stage. An elevation supporting member is located on the rotation supporting member rotatably supported by a bearing in the θ z direction. A pair of the Z axis actuators is located in a circumferential edge part of the elevation supporting member. A z axial guide part is located in the center of the elevation supporting member and guides the wafer holding member so as to go up or down with the wafer holding member.
In the above-mentioned stage apparatus, a pair of the Z axis actuators is located at the elevation supporting member rotatably supported by the bearing. Therefore, the reaction force from the Z axis actuator is applied to the elevation supporting member by driving forces of a pair of the X axis actuators.
Since the elevation supporting member is rotatably supported by the bearing, if values of two reaction forces from a pair of the Z axis actuators are different from each other, or timings of application of two reaction forces are not consistent with each other, the elevation supporting member may be oscillated in a state where the bearing is a fulcrum of the oscillation.
Such movement of the elevation supporting member due to the reaction forces from the X axis actuators may cause an error when the relative position between the wafer and an optical system is adjusted in a fine manner.
On the other hand, when a coarse moving operation of the wafer holding member in the Z axial direction is done, the driving force is large and therefore a reaction force is also large. Because of this, a mechanical natural vibration (characteristic vibration) of the elevation supporting member and XY stage where the elevation supporting member is mounted may be induced.
In this case, settling time until the vibration of the elevation supporting member due to the reaction force of the coarse moving control is dissipated may be long so that the micro moving control in the Z axial direction is delayed.